In an attempt to delay the Allied advance toward Rome, Italy, German forces set up a series of defensive lines, collectively called the Winter Line, that began with the southern-most Volturno Line to the northern-most Rome Switch Line, with the Gustav Line intending to be the strongest. The Winter Line was mainly constructed by members of the German Organization Todt, featuring many gun pits, concrete bunkers, machine gun nests, minefields, and other defensive structures, manned by troops of 15 German divisions.
In the first week of Oct 1943, British infantry crossed the Biferno River on the Adriatic Sea coast of Italy, reaching the eastern end of the southern-most Volturno Line, also known as Viktor Line; a German armor counterattack on 4 Oct nearly pushed the infantrymen back across the river, but British engineers were able to set up a bridge in time to bring up Canadian and British tanks to the front to counter the German counterattack. By 6 Oct, the territory lost to the German counterattack was regained, and the British and Canadian troops would gradually push north toward the Barbara Line. On the western end of the Volturno Line, the US 5th Army crossed the Volturno River during the night of 12 Oct, and advanced through a series of delay action engagements.
The next defensive line, Barbara Line, was reached by Allies on 2 Nov, near-simultaneously on the Tyrrhenian Sea coast by US 5th Army and on the Adriatic Sea coast by British 8th Army. In early Dec, on the western side, German troops fell back to the intermediate Bernhardt Line, also known as Reinhard Line, while on the eastern side the Germans fell back to the main Gustav Line.
